The present invention relates to the removal of sulfur from a hydrocarbon feedstock, particularly the removal of extremely small quantities of thiophene sulfur.
Generally, sulfur occurs in petroleum and syncrude stocks as hydrogen sulfide, organic sulfides, organic disulfides, mercaptans, also known as thiols, and aromatic ring compounds such as thiophene, benzothiophene and related compounds. The sulfur in aromatic sulfur-containing ring compounds will be herein referred to as "thiophene sulfur".
Conventionally, feeds with substantial amounts of sulfur, for example, those with more than 10 ppm sulfur, have been hydrotreated with conventional catalysts under conventional conditions, thereby changing the form of most of the sulfur in the feed to hydrogen sulfide. Then, the hydrogen sulfide has been removed by distillation, stripping or related techniques. Unfortunately, these techniques often leave some traces of sulfur in the feed, including thiophene sulfur, which is the most difficult type to convert.
Such hydrotreated naphtha feeds are frequently used as feeds for catalytic dehydrocyclization, also known as reforming. However, some of the catalysts used in reforming are extremely sulfur sensitive, particularly those that contain zeolitic components. Other catalysts, on the other hand, can tolerate sulfur at the levels found in typical reforming feeds.
One conventional method for removing residual hydrogen sulfide and mercaptan sulfur is the use of sulfur sorbents. See, for example, U.S. Pat. Nos. 4,204,997 and 4,163,706, the contents of which are hereby incorporated by reference. The concentration of sulfur in this form can be reduced to considerably less than 1 ppm by using the appropriate sorbents and conditions, but it has been found to be difficult to remove sulfur to less than 0.1 ppm, or to remove residual thiophene sulfur. See, for example, U.S. Pat. No. 4,179,361 the contents of which is hereby incorporated by reference, and particularly Example 1 of that Patent. Very low space velocities are required, to remove thiophene sulfur, requiring large reaction vessels filled with sorbent. Even with these precautions, traces of thiophene sulfur still can be found.
Therefore, it would be advantageous to provide a process which can remove most sulfur, including thiophene sulfur, from a reforming feedstream.